So far, for example, Patent Document 1 discloses a valve timing control apparatus of an internal combustion engine which includes a variable valve mechanism that makes changeable a valve overlap period, during which an intake valve open period overlaps with an exhaust valve open period, by changing the valve timing of at least one of the intake and exhaust valves. In this conventional control apparatus, arrangement is made such that the valve timing of intake and exhaust valve is changed such that an exhaust-port arrival timing of a negative pressure wave caused by exhaust pressure pulsation coincides with the valve overlap period of the intake and exhaust valves. According to such control, it becomes possible to make fresh air easily flow into a cylinder from the intake valve and to expel the burnt gas in the cylinder securely using the air that flowed in through the intake valve. That is, a scavenging effect can be achieved. As a result, the quantity of residual gas is reduced and the quantity of fresh air to be taken into a cylinder can be increased. That is, volumetric efficiency can be improved.
Including the above-mentioned document, the applicant is aware of the following documents as a related art of the present invention.    [Patent Document 1] Japanese Laid-open Patent Application Publication No. H11-022499    [Patent Document 2] Japanese Laid-open Patent Application Publication No. H10-176558    [Patent Document 3] Japanese Laid-open Patent Application Publication No. H11-082074    [Patent Document 4] Japanese Laid-open Patent Application Publication No. 2004-137982    [Patent Document 5] Japanese Laid-open Patent Application Publication No. 2007-100607